The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
Orthogonal frequency-division multiplexing (OFDM) is often used to encode data on multiple carrier frequencies to improve data transmission performance under undesirable channel conditions. The current IEEE 802.11ax standard has adopted a 4×OFDM symbol duration to improve data efficiency. The longer data symbol, however, can often result in heavier processing complexity at the receiver. To help the receiver to process the longer data symbol with as little processing logic overhead as possible, a signal extension (SE) of multiples of 4 μs can be used to allow additional processing time at the receiver before the next data symbols is received. Further discussion of SE with OFDM data symbols can be found in U.S. application Ser. No. 14/728,802, entitled “High Efficiency Orthogonal Frequency Division Multiplexing (OFDM) Physical Layer (PHY),” filed on Dec. 3, 2015, which is herein expressly incorporated by reference.
Padding bits can be added to the last OFDM symbol according to the SE. For example, SE can be set to be a×4 μs where a=1, 2, 3 or 4. In this case, the useful bits in the last OFDM symbol may be determined based on a×¼ of NCBPS, where NCBPS denotes the number of coded bits per symbol. When NCBPS is not multiples of 4, some modulation coding selection (MCS) scheme and SE combinations may lead to setting the number of padding bits to a non-integer number that is generally difficult, if not at all impossible, to implement.